WASHINGTON — Activists urged the government Tuesday to let people post and track cancer cases across communities, a public health effort they say could lead to discoveries of new chemical-related cancer clusters throughout the United States as well as insights into disease management.

A doctor, a cancer survivor and environmental advocate Erin Brockovich told a Senate panel that no federal agency effectively tracks cancers now in a way that easily allows scientists to determine the existence of cancer clusters.

The Senate Environment and Public Works Committee took testimony on legislation that’s aimed at helping communities determine whether there’s a link between clusters and contaminants in the environment. Clusters are occurrences of cancer in a small area or a short period of time at rates higher than statistically normal. It’s difficult to link a cluster of cancers to a particular toxin or effect, however.

Committee Chairwoman Barbara Boxer, D-Calif., and Sen. Mike Crapo, R-Idaho, are co-sponsoring the legislation, which also calls for a stronger and more coordinated federal response to investigating suspected disease clusters and documenting them, led by the Environmental Protection Agency.

Brockovich called the system for investigating and identifying disease clusters inadequate. She’s best known for fighting for the people of Hinkley, who were exposed to chromium-6 in their drinking water, an effort chronicled in a film starring Julia Roberts. At Tuesday’s hearing, Brockovich pointed to a map of potential cancer clusters that people across the country have reported to her because she’s a well-known environmental advocate and they had no one else to turn to.

An economist who testified at the request of Sen. James Inhofe of Oklahoma, the top Republican on the committee, said he was concerned about how the bill defined disease clusters. There’s “no credible way” for the EPA to set scientific priorities for identifying clusters, said Richard Belzer of Regulatory Checkbook, a Virginia organization that focuses on how scientific and economic information is used in public decision-making.